Method of excitation for electroluminescent material



NOV. 12, 1957 M, SACKS 2,813,229

METHOD OF EXCITATION FOR ELECTROLUMINESCENT MATERIAL Filed Jan. 31, 1956 2 Sheets-Sheet 1 INVENTOR. JACOB M. SACKS ATTORNE'YS Nov. 12, 1957 J. M. SACKS 2,813,229

METHOD OF EXCITATION FOR ELECTROLUMINESCENT MATERIAL Filed Jan. 31, 1956 2 Sheets-Sheet 2 INVENTOR- JACOB M. SACKS BY W ATTORNEYS METHOD OF EXCITATION FDR ELECTRO- LUMINESCENT MATERIAL Jacob M. Sacks, Corona, Calif assignor to the United States of America as represented by the Secretary of the Navy Application January 31, 1956, Serial No. 562,616

15 Claims. (Cl. 315-163) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a method and apparatus for excitation of electroluminescent material and more particularly to simple and efficient means for rapidly firing and extinguishing electroluminescent elements under the control of electronically or mechanically generated voltage or current gates thus providing for high speed readout from electronic computers, data handling equipment, or other devices requiring high speed presentation of numeric, alphabetic, or other symbolic information.

Numerous prior methods have been utilized for display and recording of numbers, letters and other symbols, such as printers, edge lighting of numerals formed in plastic, cathode glow tubes, charactron tubes, and other cathode ray displays. However, certain of these prior methods were extremely slow in operation and were limited to a relatively low speed input of symbols and other faster systems required extremely complicated apparatus or did not provide sufficient illumination of the characters, particularly for photographic recording. While various means have been used for exciting electroluminescent material, these have not been sufficiently rapid or did not provide adequate emission of light, particularly for photographic recording.

The present invention consists broadly of electronic means for rapidly firing and extinguishing electroluminescent elements, each of which may represent a separate character or one portion of a matrix adapted to form different characters by the combination of elements illuminated. This is accomplished by applying a pulse of energy to the input of a cathode follower stage using a transformer coupling to feed the energy to all of the grids of a series of parallel connected tubes, and having the electroluminescent elements forming part of a series tuned circuit in the plate circuit of each tube. A negative gating pulse is also applied to the grids of certain of the driver tubes. The gates are selectively applied to the grids of certain tubes to prevent the glow of the corresponding elements and therefore only those elements to which a gate is not applied are excited, thus illuminating the desired characters or portions of the matrix to form the character. These gates may be derived from any suitable conventional computer circuitry.

One object of the present invention is to provide simple and efficient means for the excitation of electroluminescent elements.

Another object of the present invention is to provide means for efficiently utilizing electroluminescent materials as display devices for higher speed readout for electronic computers, data handling equipment and other devices requiring high speed presentation of numeric, alphabetic or other symbolic information.

A further object of the present invention is to provide simple electronic circuitry for rapidly firing and extinguishing electroluminescent elements under the control rates Patent 2,813,229 Patented Nov. 12, 1957 ice 2 of electronically or mechanically generated voltage or current gates.

Still another object of the present invention is to provide a simple and eflicient circuit for exciting electroluminescent elements and which provides a relatively high light output suitable for photographing with simple optics.

A still further object of the present invention is to provide an electronic circuit for exciting electroluminescent elements which is high speed in operation. has low power consumption and requires only simple equipment for gating of the driving circuits for the elements.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is a schematic circuit diagram illustrating one preferred form of the present invention;

Fig. 2 is a diagram illustrating the waveform of a typical burst of high frequency energy which is applied to the control tube circuit in coincidence with. the gating pulses to the driver tubes;

Fig. 3 is a diagram illustrating the waveform of the gating pulse which is applied selectively to any desired driver tubes;

Fig. 4 is a diagram illustrating the waveform of the energy burst as it appears across the transformer of the control circuit and at the grids of the driver tubes;

Fig. 5 is a diagram illustrating the waveform of the energy as it appears across the electroluminescent element; and

Fig. 6 is a schematic circuit diagram of one preferred modification of the present invention.

Referring now to the drawings in detail, and with particular reference to Fig. 1 and the waveforms illustrated in Figs. 2 through 5, a burst of high frequency energy such as 10 kc., as illustrated in Fig. 2, is applied to the grid 11 of the control tube 12 causing a similar burst to appear at the cathode 13. The burst appears at the secondary of transformer 14 and is coupled through a resistor network to the grids of the tubes 15 and as manyothers as may be desired to complete the matrix to form a character or the series of characters desired. A typical burst as it appears on the grid of a driver tube has a waveform as: illustrated in Fig. 4. The resistors such as 17 limit grid current in the driver tubes and prevent the grid from going positive. Therefore, the grid swings between zero and cutoff. In the absence of a burst the driver tubes 15 are cut off, thus providing for efficient operation by reducing plate current.

The plates of the driver tubes 15 are connected to a plate supply such as a source of positive potential through the plate chokes 13. It is thus possible to make use of lower supply voltages than would be possible if plate load resistors were used. Resistors are connected across the plate chokes to damp out transients caused by shock excitation of the plate chokes, when the driver tubes 15 are gated off.

It has been shown that electroluminescent elements act like a low Q capacitor in which the resistive component represents a dissipation of energy in a form of light and heat. Therefore, in order to develop enough voltage across the element (which has been found to be about 1500 volts peak to peak for a particular specimen) to cause it to glow with enough intensity to photograph, it is possible to use the element as a capacitor in a series resonant circuit. The combination of a variable inductor 21 and the electroluminescent element 22 forms such a series resonant circuit. The large capacitor such as the one indicated at 23 serves merely to isolate the electroluminescent element 22 from the D. C. plate supply voltage. At a certain frequency such as 10 kc., the de lay time of a particular element 22 was found to be roughly equal to one-half cycle of the excitation frequency. Operation at this frequency resulted in a maximum of light intensity from the element, since recombination in the phosphor has just sufficient time to go .to completion. The Q of'one particular circuit tested was about 10.

In order to prevent the glow of any particular element it is necessary to apply a negative gate of about 30 volts to the terminal indicated at 24. This provides a means. of selecting the desired elements for display, and the gating pulses could be of any type derived from conventional computer circuitry or any other available source by means well known in the prior art, and could be positive or negative depending on the characteristics of the specific driver circuit.

Diode 25 merely prevents any positive voltage from appearing on the grid of the driver tube 15, and the resistor network comprising the resistors 17 and 26 isolates the gate terminal 24 from the excitation transformer 14 thus preventing interaction. The inductor 21 has been made variable so that the circuit can be tuned to resonance with the excitation frequency. It may be more convenient under certain circumstances, however, to tune the. circuit by means of a series or shunt. variable capacitor. The Waveform of the energy excitation appearing across the elements, such as 22, when it is glowing, is illustrated in Fig. 5 which is a reproduction of oscillograms made during operation of the circuit illustrated in Fig. 1.

It will be apparent that other similar stages may be connected to the secondary of the transformer 14 in parallel with the driver tube circuits illustrated tocon trol any desired number of electroluminescent elements representing any desired characters or portions of a matrix to form a particular character.

One modification of the circuit illustrated in Fig. 1 is shown in Fig. 6 wherein the secondary of the transformer 14 is shown connected to a driver circuit for one of the electroluminescent elements through a resistor 31.

In this modification it is possible to achieve substantially the same results as those obtained from the circuit of Fig. 1 by using a step-up transformer 32 in the plate of the driver tube 33' with the electroluminescent element 34 tuning the secondary of the transformer 32 to resonance. A variable condenser 35 has been utilized for tuning or adjusting the resonant circuit to resonance with the excitation frequency. In this circuit a gating pulse is likewise applied to a terminal 36 and through a resistor 37 to the grid of the tube 33 with a diode 38 provided to prevent any positive voltage from appearing on the grid of the tube 33. A resistor 39 is also providedin parallel with the primary of the transformer 32 to damp out transients caused by shock excitation of the plate load consisting of the primary of the transformer 32 when the tube 33 is gated off.

The circuits of the present invention provide a relatively high light output in the electroluminescent elements which is suitable for photographing with only simple optics required. The circuitry involved is simple, it is high speed in operation and has a low power consumption. Furthermore, the equipment required for gating the circuit (not shown) may also be extremely simple in nature or it can be any desired output from a suitable electronic computer.

()bviously many modifications and variations of the, present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An electronic circuit for the excitation of a series of electroluminescent elements comprising an electronic control circuit adapted to receive a burst of energy, said control circuit being operatively associated with a plurality of driver circuits, and a resonant circuit operatively 4 associated with each of said driver circuits, said resonant circuits each including an electroluminescent element.

2. An electronic circuit for the excitation of a series of electroluminescent elements comprising an electronic circuit adapted to receive a short burst of energy, said circuit being operatively associated with a plurality of driver tubes, a resonant circuit operatively associated with each of said driver tubes, said resonant circuits each including an electroluminescent element, and means for applying a gating voltage to each of said driver tubes.

3. An electronic circuit for the excitation of a series of electroluminescent elements comprising a cathode follower circuit having. a tube adapted to receive a short burst of high frequency energy on the grid thereof, said circuit being operatively associated with the grids of a plurality of driver tubes, a load in the plate circuit of each of said driver tubes, a resonant circuit operatively associated with the plate circuit of each of said driver tubes, said resonant circuits each including an electroluminescent element acting as a low Q capacitor therein, means for adjusting the resonant frequency of said resonant circuits to the excitation frequency, and means for applying. a gating voltage to each of the grids of said driver tubes.

4. An electronic circuit for the excitation of a series of electroluminescent elements comprising a cathode follower circuit having a tube adapted to receive a short burst of high frequency energy on the grid thereof and the primary of a transformer between the cathode and ground, the secondary of said transformer being operatively associated with the grids of. a plurality of driver tubes through a resistor network, an inductive load in the plate circuit of each of said driver tubes, a resonant circuit operatively associated with the plate circuit of each of said driver tubes, said resonant circuits each including an electroluminescent element acting as a low Q capacitor therein, and means for adjusting the resonant frequency of said resonant circuits to the excitation frequency, and means for applying agating voltage to each of the grids of said driver tubes.

5. An electronic circuit for the excitation of a series of electroluminescent elements comprising a cathode follower circuit having a tube adapted to receive a short burst of high frequency energy on the grid thereof and the primary of a transformer between the cathode and ground, the secondary of said transformer being operatively associated with the grids of a series of driver tubes through a resistor network, an inductive load in the plate circuit of each of saiddrivertubes, aseries resonant circuit operatively associated with the plate circuit of each of .said driver tubes,,said series resonantcircuits each including an electroluminescent element acting as a low Q capacitor therein, and means for adjusting the resonant frequency of said: resonant circuits to the excitation frequency, and means for applying a gatingvoltage to each of the grids of said. driver tubes.

6. An electronic circuit for exciting aseriesof electroluminescent elements selectively comprising a control tube having a grid adapted toreceive a high frequency burst and a cathode circuit including the primary of a transformer, the secondary of said transformer being connected to a plurality of parallel circuits each including a driver tube having a grid adapted to receive a signal burst from the secondary of said transformer, each of saiddriver tubes having an inductive plate load connected to a plate supply voltage, an electroluminescent element in a series resonant circuit with an inductance and connected to said plate load and ground, a resistance and a diode between the grid of each of said driver tubes and ground, and a' terminal between said last resistance and said diode adapted to receive a gating pulse from suitable control equipment in coincidence with said high frequency burst for selectively actuating and illuminating certain of said electroluminescent elements.

7'. An electronic circuit for exciting a series of electroluminescent elements selectively comprising a control circuit connected to a plurality of parallel driver circuits, each of said driver circuits including a driver tube having a grid adapted to receive a signal burst from said control circuit, each of said driver tubes having a plate choke adapted to be connected to a source of positive potential, a condenser connected to the plate of each of said driver tubes, and an electroluminescent element in series with said condenser and connected to the ground.

8. An electronic circuit for exciting a series of electroluminescent elements selectively comprising a control circuit connected to a plurality of parallel driver circuits, each of said driver circuits including a driver tube having a grid adapted to receive a signal burst from said control circuit, each of said driver tubes having a plate choke adapted to be connected to a source of positive potential, a condenser connected to the plate of each of said driver tubes, an electroluminescent element in series with said condenser and connected to the ground, a resistance and a diode between the grid of each of said driver tubes and ground, and a terminal between said last resistance and said diode adapted to receive a gating pulse from suitable control equipment in coincidence with said high frequency burst for selectively actuating and illuminating certain of said electroluminescent elements.

9. An electronic circuit for exciting a series of electroluminescent elements selectively comprising a control tube having a grid adapted to receive a high frequency burst and a cathode circuit including the primary of a transformer, the secondary of said transformer being connected to a plurality of parallel circuits, each of said circuits including a driver tube having a grid adapted to receive a signal burst from the secondary of said transformer, each of said driver tubes having a plate choke adapted to be connected to a source of positive potential,

a condenser connected to the plate of each of said driver.

tubes, a variable inductance in series with said condenser, an electroluminescent element in series with said variable inductance and connected to the ground, a resistance and a diode between the grid of each of said driver tubes and ground, and a terminal between said last resistance and said diode adapted to receive a gating pulse from suitable control equipment in coincidence with said high frequency burst for selectively actuating and illuminating certain of said electroluminescent elements.

10. An electronic circuit for exciting a series of electroluminescent elements selectively comprising a control tube having a grid adapted to receive a high frequency burst and a cathode circuit including the primary of transformer, the secondary of said transformer being connected to a plurality of parallel circuits each including a driver tube having a grid adapted to receive a signal burst from the secondary of said transformer, each of said driver tubes having a plate choke adapted to be connected to a source of positive potential, a resistance shunted across said plate choke, a condenser connected to the junction between said plate choke and the plate of each of said driver tubes, a variable inductance in series with said condenser, a-n electroluminescent element in series with said variable inductance and connected to ground, a resistor between the grid of each of said driver tubes and the secondary of said transformer, a resistance and a diode between the grid of each of said driver tubes and ground, and a terminal between said last resistance and said diode adapted to receive a gating pulse from suitable control equipment in coincidence with said high frequency burst for selectively actuating and illuminating certain of said electroluminescent elements.

11. An electronic circuit for exciting a series of electroluminescent elements selectively comprising a control circuit, a plurality of driver tubes each having their control grids connected to said control circuit, a transformer having its primary in the plate circuit of each of said driver tubes, and an electroluminescent element in parallel with the secondary of said plate transformer.

12. An electronic circuit for exciting a series of electroluminescent elements selectively comprising a control circuit, a plurality of driver tubes each having their control grids connected to said control circuit, a transformer having its primary in the plate circuit of each of said driver tubes, an electroluminescent element in parallel with the secondary of said plate transformer and means for adjusting the resonant frequency of the circuit including said electroluminescent element.

13. An electronic circuit for exciting a series of electroluminescent elements selectively comprising a cathode follower circuit, a transformer having its primary in the cathode circuit of said cathode follower, said cathode follower circuit including a control grid adapted to receive a burst of high frequency energy, a series of driver tubes each having their control grids connected to the secondary of said transformer, a transformer having its primary in the plate circuit of each of said driver tubes, an electroluminescent element in parallel with the secondary of said plate transformer, a variable condenser in parallel with said electroluminescent element, and means for applying a gating pulse to the grids of certain of said tubes.

14. An electronic circuit for exciting a series of electroluminescent elements selectively comprising a cathode follower circuit, a transformer having its primary in the cathode circuit of said cathode follower, said cathode follower circuit including a control grid adapted to receive a burst of high frequency energy, a plurality of driver tubes each having their control grids connected to the secondary of said transformer, a transformer having its primary in the plate circuit of each of said driver tubes, an electroluminescent element in parallel with the secondary of said plate transform-er, a variable condenser in parallel with said electroluminescent element, and means for selectively applying a gating pulse to the grids of certain of said tubes for selectively actuating certain of said electroluminescent elements.

15. An electronic circuit for exciting a series of electroluminescent elements selectively comprising a cathode follower circuit, a transformer having its primary in the cathode circuit of said cathode follower, said cathode follower circuit including a control grid adapted to receive a burst of high frequency energy, a plurality of driver tubes each having their control grids connected to the secondary of said transformer through an isolating resistor, a transformer associated with each of said driver tubes and having its primary in the plate circuit thereof, a resistor shunted across the primary of said transformer, an electroluminescent element in parallel with the secondary of said plate transformer, a variable condenser in parallel with said electroluminescent element, and means for selectively applying a gating pulse to the grids of certain of said tubes for selectively actuating certain of said electroluminescent elements.

References Cited in the file of this patent UNITED STATES PATENTS 2,583,146 Jacob Jan. 22, 1952 2,601,491 Baker June 24, 1952 2,679,617 Mullaney et a1 May 25, 1954 2,694,785 Williams Nov. 16, 1954 

